TSH high or low? What your thyroid test is telling you.

About 1 in 10 Indian adults has an underactive thyroid, and a third don’t know it. Here’s how to read the report, and why a borderline number deserves a retest first.

7 min read · Updated 11 Nov 2026

A woman smiles as she reads a folded sheet of paper at a wooden table, with a cup of chai and her glasses beside her.

The short version

1
TSH is the main number, and it works in reverse: high TSH usually means an underactive thyroid, low TSH an overactive one.⁸
2
A mildly high TSH with a normal T4 is worth repeating in 2–3 months: more than half of people with 5.5–10 were normal on retest.^20,22
3
There’s no special “thyroid diet”. Cooked cabbage, soy and millets are fine; use iodised salt.^6,24,26,28

Your number

Where does your TSH sit?

Slide the dot to the TSH on your report.

Your TSH

6.2mIU/L

Mildly high

With a normal free T4, this is “subclinical”. Repeat TSH, free T4 and anti-TPO in 2–3 months before deciding anything.

Slide to your own number. TSH in mIU/L, the same as µIU/mL. Not for pregnancy, which has its own ranges.^13,19,20

Your report

Read TSH together with T4

High TSH, low free T4: An underactive thyroid (primary hypothyroidism).
High TSH, normal free T4: Subclinical: mild or early. Repeat the test before acting on it.
Low TSH, high free T4: An overactive thyroid (hyperthyroidism).
Low TSH, normal T4, high T3: Some overactive thyroids show only a high T3.
Low TSH, low free T4: A problem in the pituitary gland, not the thyroid (secondary hypothyroidism).
Normal TSH and T4, positive anti-TPO: Thyroid autoimmunity. No treatment is needed; keep checking TSH over time. In one long UK study, about 2% a year went on to an underactive thyroid.^10,19,23

TSH is the best first test. Free T4 is more reliable than total T4 in pregnancy or on the pill, and T3 rarely helps with an underactive thyroid. Free T4 usually runs about 0.8–1.9 ng/dL (10.3–24.5 pmol/L).^8,14,15,20

India

One in ten, and many don’t know

1 in 10: adults in eight Indian cities had an underactive thyroid, and about a third of them didn’t know it.¹
15.9%: of women had it, against 5.0% of men.¹
21.9%: tested positive for anti-TPO antibodies.¹

Pooled studies project about 42 million Indians with thyroid disease. Healthy Delhi adults averaged a TSH of 2.2.^2,3

Borderline?

Retest before you’re labelled

How often a raised TSH was normal on the next test, among 346,549 people not on thyroid medicine.

First TSH 5.5–1062% normal on retest
First TSH above 1027% normal on retest

An Israeli health database. When the first TSH was normal, 98% stayed normal over 5 years.²²

The European Thyroid Association advises repeating TSH, free T4 and anti-TPO after 2–3 months. A 2019 BMJ guideline, drawing on 21 trials, recommends against thyroid hormone for most adults with subclinical hypothyroidism: it didn’t help tiredness, mood, quality of life or weight. It doesn’t cover women trying to conceive or a TSH above 20. Never stop or change a medicine without your doctor.^20,21

Testing

Getting a reliable result

2 days before
Pause biotin
Biotin supplements can throw the result off.⁸
The day
Test in the morning
TSH runs highest early in the day and can swing by about 1–2 mIU/L across it.^13,19
After an illness
Wait a few weeks
TSH can dip during an illness and rise as you recover.¹⁹
Every repeat
Same lab if you can
Ranges differ between labs and machines. Once on treatment, doctors usually recheck 6–8 weeks after any change.^19,20

Pregnancy

If you’re pregnant or planning to be

TSH ranges change in each trimester, and Indian sources don’t agree.

First trimester: MoHFW 2014: 0.1–2.5. Healthy pregnant women in Delhi: 0.6–5.0.
Second trimester: MoHFW 2014: 0.2–3. Delhi study: 0.44–5.78.
Third trimester: MoHFW 2014: 0.3–3. Delhi study: 0.74–5.7.

That’s why your doctor uses trimester-specific ranges. Indian studies find an underactive thyroid in 4.8–12% of pregnancies. Already on thyroid medicine? Get your TSH checked as soon as the pregnancy is confirmed.^4,5,12

Food and weight

What you might hear

They say
“Never eat cabbage or cauliflower with a thyroid problem.”
Actually
Most of the cabbage family, broccoli included, carries little risk. The famous harm was one case of very large amounts of raw bok choy. Normal cooked portions are fine.^28,29
They say
“Soy is banned.”
Actually
Fourteen trials found little or no effect on thyroid function when iodine intake is adequate. Soy may change how much medicine you need, so tell your doctor, but you don’t have to avoid it.²⁴
They say
“Everyone with Hashimoto’s must go gluten-free.”
Actually
A meta-analysis found the evidence isn’t enough to recommend it for everyone.²⁵
They say
“Millets cause goitre.”
Actually
A systematic review found the evidence not compelling for bajra eaten as part of a balanced diet.^26,27
They say
“Thyroid tablets will make me thin.”
Actually
Expect about 2–4.5 kg, mostly water. After that, weight works as it does for anyone.^11,30
They say
“Positive anti-TPO means I need medicine now.”
Actually
Not if TSH and free T4 are normal. Keep checking TSH.^10,16

Losing weight with a thyroid condition follows the usual rules: ICMR-NIN advises about 0.5 kg a week, never below 1,000 calories a day, and no crash diets. Keep using iodised salt; 94.3% of Indian homes already do. Our Indian weight-loss plan works the same way.^6,7

See a doctor soon if

You’re pregnant or planning a pregnancy, and any thyroid result is off.
An older person with an underactive thyroid becomes very drowsy, cold or confused. This is a rare emergency.
A swelling in your neck makes it hard to breathe, or you wheeze: get emergency care. Trouble swallowing or a hoarse voice also needs a doctor.
Your TSH is above 10, or your free T4 is low.
On treatment, you feel nervous or hot, your heart races, or you lose weight without trying.

Don’t start, stop or change thyroid tablets without your doctor.

Warning signs from the American Thyroid Association, the NHS and the European Thyroid Association.^{1,5,9,12,17,18,20}

Questions

Questions people ask

Thyroid mein kya nahi khana chahiye? (What should I avoid eating with a thyroid problem?)

Very little. Cooked cabbage, cauliflower and broccoli, soy, millets and roti are fine in normal amounts, and you should use iodised salt. What matters more is taking your tablet the way your doctor says, away from calcium or iron supplements.

What is a normal TSH level?

Often about 0.4–4.5 mIU/L, but every lab differs. Older people and pregnant women have different ranges, so go by the range on your report.

My TSH is 6 and my T4 is normal. Do I have thyroid disease?

That pattern is called subclinical hypothyroidism. Repeat the test in 2–3 months: more than half of people with a TSH of 5.5–10 are normal on retest. Most adults with it are not treated.

What does a positive anti-TPO test mean?

Your immune system is reacting to your thyroid. It’s common: 21.9% of adults in an eight-city Indian study. If your TSH is normal, no treatment is needed; get TSH checked from time to time.

Will treating my thyroid make me lose weight?

Usually only a few kilos, mostly water. After that, losing fat works the same as for anyone else.

When is the best time to get a thyroid test?

In the morning. Stop biotin supplements 2 days before, and avoid testing during or just after an acute illness.

Sources

Swastya shares health education, not medical advice. Lab ranges vary by lab, age and condition, so read your numbers with your doctor, and see a doctor promptly for any symptom that worries you.

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